here is the circuit. as you can see I have an input voltage of -48VDC and i'm trying to have that send a high signal to the arudino when the 48 V signal is lost. the problem is for a circuit that will be in the ON state for most it's life .7Watts of heat across R1 is just too high.

Because when you have 115 channels of this the total heat on the circuit board will be over 80 Watts dissipated. And i'm not trying to build a heater =) I could use relays but i wanted the solid state reliability.

The input current per channel is only 10uA worst case so you can use a voltage divider with large value resistors to minimize power. The unit does need a ~2mA power supply though, but you will still probably come out ahead as it has 4 channels so it's really only 500uA per channel.

What kind of linearity are you getting with the optocoupler? I was thinking of going with the LOC110 which is supposed to be linear but I haven't received it yet. The regular opto couplers suffers from non-linear outputs thus not recommended for ADCs.

The problem I have is being able to measure -48 v systems and +24v systems with one unit. Altho I found a solution for that(relays, voltage inverter), I am still looking for alternate solutions.

I've run the input voltage from 18-54 on both a positive +24V system and -48V system and still had a stable TTL logic out of it using that 33K resistor. I know it's under driving the current at that point but it still works great.